Telephones are conventioanlly constructed with a base unit which is connected to the telephone wires by a cable extending to the telephone outlet in the wall adjacent the telephone location. The base unit functions with a hand unit that is connected to the base unit by means of a cord and is not considered portable. The hand unit is restricted in its portability by the length of the cord connecting it to the base unit. The base unit may be fixed in position, or moveable within the restrictions of a telephone cable connecting it to the telephone outlet. The hand unit is usually stored on the base unit and mechanically operates a hook switch on the base unit as a result of its placement on or removal from the base unit. The operation of the hook switch controls the transmission over the telephone in accordance with its operating position. When the hand unit is mounted on the cradle of the base unit, the telephone is considered always on hook. The operation of the hook switch of the base unit by removing the hand unit from the base cradle is considered as an off hook condition and permits transmission over the telephone or permits an individual to speak into the hand unit. The placement of the hand unit back on the base unit cradle operates the hook switch for terminating transmission over the telephone. A conventional corded telephone may have the controls in either the base unit or hand unit.
In recent years cordless telephones have been manufactured and sold in large numbers. A cordless telephone also comprises a base unit and a handset, except that the handset is not connected to the base unit by a cord and may be carried a substantial distance from the base unit and still be operative therewith. Present day cordless telephones utilize electromagnetic radiation in the radio frequency range to couple the telephone signals between the base unit and the handset. For this purpose both the base unit and the handset are provided with electronic signal transmitters and electronic signal receivers that are responsive to a preselected radio frequency signal. The handset also usually contains all controls, such as a dial or buttons, to operate the cordless phone. The handset also includes a "talk" switch which must be operated when the handset is not mounted on the base unit so as to control the "off hook" condition or the ability to transmit telephone signals. When the handset is removed from the base unit, then, it is necessary to operate the talk switch to "On" to provide the "off hook" condition to allow transmission, or an individual to speak into the hand unit. When transmission is to be terminated the talk switch is operated to "Off" or the handset is placed back on the base unit so as to operate the hook switch, or to the "on hook" condition.
The cordless telephone has been found to have many problems in its use that are not found in the corded telephone. The problems that have been noted are that the cordless telephone does not have as much voice security as the conventional corded telephone, and noise can cause a false ringing of a cordless phone, and there is a possibility that another handset for a cordless telephone operating on the same frequency can capture the base unit and make an unauthorized telephone call through a neighbor's base unit. These problems, of course, can be corrected by the use of a corded phone. The advantage of the cordless phone is that one does not have to be in the immediate vicinity of the base unit to receive a telephone call, but the phone will ring at the handset as long as it is within the transmission range of the base unit electronic transmitting means. Accordingly, there is a need for a telephone that solves the problems of a cordless phone and yet has the advantages of a corded telephone along with the advantages of a cordless telephone.